The present invention relates to an alignment method, alignment apparatus, and profiler suitable for alignment and the like in a semiconductor manufacturing exposure apparatus between a microelectronic circuit pattern, e.g., an IC, LSI, or VLSI, formed on a reticle surface and a wafer, an exposure apparatus, semiconductor device manufacturing method, and semiconductor manufacturing factory using the alignment method, alignment apparatus, and profiler, and an exposure apparatus maintenance method.
Most exposure apparatuses currently used are called steppers or scanners. In this specification, the steppers and scanners are not discriminated, but are also described as xe2x80x9cexposure apparatusesxe2x80x9d for descriptive convenience unless they need to be specifically discriminated.
As integrated circuits shrink in feature size and increase in integration degree, a semiconductor manufacturing projection exposure apparatus must be able to project and expose a circuit pattern on a reticle surface onto a wafer surface with a higher resolution. For this purpose, in consideration of the fact that the projecting resolution of a circuit pattern depends on the numerical aperture (NA) of a projection optical unit and the exposure wavelength, studies have been made on an exposure method in which the exposure wavelength is fixed and the NA of the projection optical unit is increased, and an exposure method in which the exposure wavelength is decreased, an i-line is preferred over a g-line and an excimer laser oscillation wavelength is preferred over the i-line wavelength, and 248- and 193-nm wavelengths, and moreover 157-nm wavelength are used as the laser oscillation wavelength. A projection exposure apparatus using a 193-nm exposure wavelength is already commercially available.
As the circuit patterns shrink in feature size, a demand for high-precision alignment between a wafer and a reticle on which an electronic circuit pattern is formed has also arisen. When aligning a reticle and wafer with each other, light (exposure light) that photosensitizes a resist applied on the wafer surface and light (to be referred to as xe2x80x9cnon-exposure lightxe2x80x9d hereinafter) that does not photo-sensitize the resist, e.g., light with a wavelength of 633-nm, which is the oscillation wavelength of an Hexe2x80x94Ne laser, are often used. Conventionally, the alignment wavelength practically employed is mostly that of the non-exposure light, because it is not easily influenced by a semiconductor manufacturing process. More specifically, since a resist to be photosensitized by exposure light is absorbed by the exposure light, the exposure light is transmitted through the resist with a low transmittance, and sometimes the exposure light is not transmitted at all. When the exposure light is used for alignment, while it passes through the resist, is reflected by an alignment mark, and passes through the resist again, it sometimes becomes very weak to be used as an alignment signal. When the exposure light interferes with light reflected by the resist surface, interference fringes are formed on the detected image, leading to degradation in precision. This is because the light is reflected by the resist surface with a reflectance of approximately 4%, and light transmitted through the resist twice also has an intensity of the same level as this, forming interference fringes with a high visibility (brightness contrast).
In view of this, in Japanese Patent Laid-Open Nos. 63-32303, 2-130908, and the like, the present applicant has also proposed an alignment apparatus using non-exposure light that is transmitted through a resist with a high transmittance. Such an apparatus is already commercially available so its effect has been confirmed. This method is a so-called non-exposure light TTL Offaxis method, in which chromatic aberration in non-exposure light of a projection optical unit for transferring and projecting a reticle pattern onto a wafer is corrected in the wavelength width as an alignment optical unit. As described in the above references, most of the currently employed alignment methods are a method of forming an optical image of an alignment mark on a wafer on an image sensing element such as a CCD camera, and image-processing an electrical signal from the image sensing element, thereby detecting the wafer position. With this method, light is not attenuated even after it is transmitted through the resist twice. Thus, even if monochromatic light is used as the non-exposure light, the interference fringes formed by interference with the light reflected by the resist surface have a low visibility (brightness contrast). In the references, since monochromatic light is not used but light with a correction wavelength width of, e.g., 70 nm or more in half width, is used, the interference fringes are suppressed to a level that does not pose any problem.
As a method of eliminating a process error called WIS (Wafer Induced Shift) as one of alignment errors, the present applicant has proposed a system called offset analyzer. As an example of WIS, the shape of the alignment mark and the shape of a resist on the alignment mark become asymmetric due to a process error. In a planarizing process in a modern metal CMP (Chemical Mechanical Polishing) step and the like, the structure of the alignment mark often becomes asymmetric. This produces a rotation error as shown in FIG. 5 or a magnification error as shown in FIG. 6 in global alignment, leading to a serious problem as a decrease in precision.
In order to eliminate degradation in precision which is caused when an alignment mark shape becomes asymmetric due to the process, in the offset analyzer, before a wafer position necessary for alignment of a wafer and reticle relative to each other is to be performed with a non-exposure light TTL offaxis alignment detection system with a highly stable base line, the surface shapes of a plurality of identical marks on the wafer which are used for alignment are measured, outside an exposure apparatus with an alignment apparatus, with a profiler (stereoscopic measurement unit) such as an AFM (Atomic Force Microscope) before and after resist coating. An offset, with which the three-dimensional relative positional relationship between the mark shapes before resist coating and those after resist coating matches with a signal from the detection system of the alignment apparatus, is calculated. Then, the wafer and reticle are aligned with each other by using the calculated offset. In this manner, a system for measuring the surface shapes of the marks before and after resist coating outside an alignment apparatus (exposure apparatus) with a profiler such as AFM, and calculating an offset with which the three-dimensional relative positional relationship between the respective mark shapes matches with a signal from the detection system of the alignment apparatus, is called an offset analyzer.
FIG. 3 shows data obtained when actual alignment marks are measured with the AFM. These data are indicated as signals displayed to correspond to respective alignment marks AM in FIG. 3. These data are those obtained after resist coating. The structures of the alignment marks AM are those called metal CMP as shown in FIG. 4. As is seen from FIG. 3, regarding the surface shapes of the alignment marks AM at shots on the left, right, and center of the wafer W, although the surface shape of the alignment mark AM of the shot at the center is symmetrical, the surface shape of each of the left and right shots is asymmetric with the asymmetry being reversed between the left and right shots. This is WIS. Even when such WIS occurs, with an offset analyzer, a highly stable alignment method can be implemented at high precision with less base line fluctuation.
A profiler used in the offset analyzer may be an AFM, a probe type profiler, or an optical non-contact type profiler. Any profiler poses no problem as far as it satisfies the specifications.
Since the resist is transparent to a wavelength used by the optical profiler, it is difficult to correctly measure the resist surface with the optical profiler. Meanwhile, for example, with an AFM, the resist surface of a measurement target as an actual sample is measured on the basis of the atomic force between the resist surface and that portion of the AFM which is called a probe. Accordingly, measurement is not influenced by the transmittance of the resist. When an optical profiler is used, a confocal detection method or a method using a wavelength corresponding zero transmittance of a resist may be employed.
In an exposure method using a KrF laser, as the planarizing technique such as CMP is introduced, the resist thickness is reduced to half (about 0.5 xcexcm) about 1 xcexcm in i-line exposure. In the confocal detection method, since the optical path length is considered in terms with geometrical optics, the refractive index of the resist is almost 1.5, so the confocal detection method must be able to separate a thickness of 0.5/1.5=0.33 xcexcm. However, a confocal detection method that can separate a thickness of 0.5/1.5=0.33 xcexcm does not exist, and even if it does exist, it must have an oil-immersion objective having a numerical aperture NA of 0.9 or more. As a result, an error in the optical unit, e.g., an eccentric coma, tends to occur, making it difficult to perform high-precision detection. If a method using a wavelength that is not transmitted through a resist is employed, as this method depends on the characteristics of the resist, it cannot measure any resist. For example, with a KrF resist, since the transmittance decreases only around the exposure wavelength, an excimer laser is used for the light source of the profiler as well. This greatly increases the cost.
From the above reasons, conventionally, in an offset analyzer, an AFM or a probe type profiler is inevitably used to measure the resist surface. The AFM, probe type profiler, and optical profiler will be described later again.
In the prior art, when an AFM or probe type profiler is used in favor of the horizontal resolution, the wafer surface may be contaminated. This is because, with an AFM or probe type profiler, when the atomic force is not used as a measurement value, the probe used for performing this measurement sometimes comes into strong contact with the wafer surface. For example, with the AFM, as the name suggests, the atomic force is used as the measurement value. As shown in FIG. 16, if an alignment mark AM of a wafer has such a shape that the distance between the AFM and the wafer decreases from the current measurement position to the next measurement point, a probe 2 of the AFM comes into strong contact with the wafer surface once, and a preset atomic force is not generated. Therefore, the probe 2 is separated after this to a position at such a distance that an atomic force can be obtained, and a measurement value is obtained. This distance often changes exceeding a value with which an atomic force is generated, although depending on the shape of the alignment. In practice, therefore, the probe 2 often comes into strong contact with the measurement surface. Then, the shape of the probe deforms and according the measurement value changes. This is one of the factors that determines the service life of the probe. The thinner the distal end of the probe, the shorter the service life.
The probe is made of a silicon-based material. Since this probe comes into strong contact with the process member of the wafer, a possibility of contamination cannot be denied. Even if contamination can be completely eliminated by washing after measurement, the washing time decreases the throughput, leading to another problem. The probe serves to measure a soft target such as a resist surface. Thus, if the probe comes into strong contact with the measurement target, it may damage the surface. In this case, the shape indicated by the measurement value and that obtained after strong contact may differ, and the original effect of the offset analyzer cannot be exhibited. In the following description, an AFM or probe type profiler will be expressed as xe2x80x9ca profiler with a contact possibilityxe2x80x9d, and a complete non-contact measurement profiler such as an optical profiler will be expressed as xe2x80x9ca profiler with no contact possibilityxe2x80x9d.
The present invention has been made in view of the above problems of the prior art, and has as its object to enable, in an alignment method, alignment apparatus, profiler, exposure apparatus, semiconductor device manufacturing method, semiconductor manufacturing factory, and exposure apparatus maintenance method, measurement of the shape of a mark without contaminating or damaging the mark.
In order to achieve the above object, an alignment method according to the present invention comprises the steps of:
in order to expose a pattern of a first object onto a second object, detecting a plurality of marks on the second object with mark detection means and aligning the first and second objects with each other;
measuring a shape of a mark on the second object before the step of aligning, thereby obtaining an offset that should be reflected in a detection result of the mark detection means,
wherein the shape of the mark is measured with shape measurement means with no possibility of coming into contact with the mark, through calibration with reference to shape measurement means with a possibility of coming into contact with the mark.
Preferably, the above alignment method further comprises, for performing the calibration, the step of measuring shapes of the plurality of marks on the second object with the shape measurement means with contact possibility.
Preferably, in the above alignment method, the shape measurement means with contact possibility comprises an atomic force microscope or a probe type stereoscopic shape measurement unit.
Preferably, in the above alignment method, measurement of the shape of the mark is performed before and after coating the second object with a resist for exposure.
Preferably, in the above alignment method, the offset is obtained based on a result obtained through correspondence between a detection signal obtained by the mark detection means and a relative positional relationship between the shape of the mark before resist coating and that after resist coating, which are measured by performing calibration with the shape measurement means with no contact possibility.
Preferably, in the above alignment method, when the second object to be exposed comprises a plurality of second objects, the second objects which follow the first one of the second objects are also aligned by using the offset obtained by using the first one of the second objects.
Also, an alignment apparatus according to the present invention comprises:
in order to expose a pattern of a first object onto a second object alignment, means for detecting a plurality of marks on the second object with mark detection means and aligning the first and second objects with each other; and
means for measuring a shape of a mark on the second object before alignment of the first and second objects, thereby obtaining an offset that should be reflected in a detection result of the mark detection means,
wherein the shape of the mark is measured with shape measurement means with no possibility of coming into contact with the mark, through calibration with reference to shape measurement means with a possibility of coming into contact with the mark.
Also, a profiler according to the present invention comprises:
first shape measurement means for measuring the shape of the mark while having a possibility of coming into contact with the mark;
second shape measurement means for measuring the shape of the mark while having no possibility of coming contact with the mark; and
calibration measurement means for performing calibration with reference to said first shape measurement means in order to measure the shape of the alignment mark with said second shape measurement means.
Preferably, in the above profiler, the calibration measurement means performs calibration based on a predetermined causal relationship, obtained by measuring the shape of the mark with the first and second shape measurement means before and after coating of the resist, while changing a coverage of the resist with respect to the mark by slightly changing a condition for a coater that coats the mark with a resist from an optimal one.
Preferably, in the above profiler the calibration measurement means performs calibration based on information concerning a thickness of the resist applied to the exposure target substrate.
Also, an exposure apparatus for exposing a pattern on a master mask onto a substrate according to the present invention, comprises:
an alignment apparatus for aligning the master mask and substrate with each other,
the alignment apparatus comprising:
in order to expose a pattern of a first object onto a second object, alignment means for detecting a plurality of marks on the second object with mark detection means and aligning the first and second objects with each other, and
means for measuring a shape of a mark on the second object before alignment of the first and second objects, thereby obtaining an offset that should be reflected in a detection result of the mark detection means,
wherein the mark is measured with shape measurement means with no possibility of coming into contact with the mark, through calibration with reference to shape measurement means with a possibility of coming into contact with the mark.
Preferably, in the above exposure apparatus, the apparatus further comprises a display, a network interface, and a computer for executing network software, and
maintenance information of the exposure apparatus can be communicated via a computer network.
Preferably, in the above exposure apparatus, the network software provides on the display a user interface connected to an external network of a factory where the exposure apparatus is installed to access a maintenance database provided by a vendor or user of the exposure apparatus, and enables obtaining information from the database via the external network.
Also, a semiconductor device manufacturing method according to the present invention comprises the steps of:
installing a plurality of semiconductor manufacturing apparatuses including an exposure apparatus at a semiconductor manufacturing factory; and
manufacturing a semiconductor device by using the plurality of semiconductor manufacturing apparatuses,
the exposure apparatus including an alignment apparatus for aligning a master mask and a substrate with each other, and
the alignment apparatus comprising:
in order to expose a pattern of a first object onto a second object, alignment means for detecting a plurality of marks on the second object with mark detection means and aligning the first and second objects with each other, and
means for measuring a shape of a mark on the second object before alignment of the first and second objects, thereby obtaining an offset that should be reflected in a detection result of the mark detection means,
wherein the shape of the mark is measured with shape measurement means with no possibility of coming into contact with the mark, through calibration with reference to shape measurement means with a possibility of coming into contact with the mark.
Preferably, the above semiconductor device manufacturing method further comprises the steps of:
connecting the plurality of manufacturing apparatuses by a local area network;
connecting the local area network to an external network outside the factory;
obtaining information about the exposure apparatus from a database on the external network by utilizing the local area network and the external network; and
controlling the exposure apparatus on the basis of the obtained information.
Preferably, in the above semiconductor device manufacturing method, a database provided by a vendor or user of the exposure apparatus is accessed via the external network to obtain maintenance information of the manufacturing apparatus by data communication, or production management is performed by data communication between the semiconductor manufacturing factory and another semiconductor manufacturing factory via the external network.
Also, a semiconductor manufacturing factory according to the present invention comprises:
a plurality of semiconductor manufacturing apparatuses including an exposure apparatus;
a local area network for connecting the plurality of semiconductor manufacturing apparatuses; and
a gateway for connecting the local area network to an external network outside the semiconductor manufacturing factory, so that information about at least one of the plurality of semiconductor manufacturing apparatuses can be communicated,
the exposure apparatus including an alignment apparatus for aligning a master mask and substrate with each other,
the alignment apparatus comprising:
in order to expose a pattern of a first object onto a second object, alignment means for detecting a plurality of marks on the second object with mark detection means and aligning the first and second objects with each other, and
means for measuring a shape of a mark on the second object before alignment of the first and second objects, thereby obtaining an offset that should be reflected in a detection result of the mark detection means,
wherein the mark is measured with shape measurement means with no possibility of coming into contact with the mark, through calibration with reference to shape measurement means with a possibility of coming into contact with the mark.
Also, an exposure apparatus maintenance method comprises the steps of:
causing a vendor or user of the exposure apparatus to provide a maintenance database connected to an external network of a semiconductor manufacturing factory;
authorizing access from the semiconductor manufacturing factory to the maintenance database via the external network; and
transmitting maintenance information accumulated in the maintenance database to the semiconductor manufacturing factory via the external network,
the exposure apparatus includes an alignment apparatus for aligning a master mask and substrate with each other,
the alignment apparatus comprising:
in order to expose a pattern of a first object onto a second object, alignment means for detecting a plurality of marks on the second object with mark detection means and aligning the first and second objects with each other, and
means for measuring a shape of a mark on the second object before alignment of the first and second objects, thereby obtaining an offset that should be reflected in a detection result of the mark detection means,
wherein the shape of the mark is measured with shape measurement means with no possibility of coming into contact with the mark, through calibration with reference to shape measurement means with a possibility of coming into contact with the mark.
In the above arrangements, the mark shape is measured with a shape measurement means with no possibility of coming into contact with the mark. In measurement, since the measurement means is subjected to calibration with reference to a shape measurement means with a possibility of coming into contact with the mark, the mark shape is measured without coming into contact with the first object. Therefore, the first object will not be contaminated or damaged.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.